TAJO-999: SequenceFile key class need to be compatible. (jaehwa)

Closes #110
TAJO-928: Session variables should override query configs in TajoConf.

Closes #98
TAJO-947: ColPartitionStoreExec can cause URISyntaxException due to special characters. (Mai Hai Thanh via hyunsik)
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo